profile: use explicit logic to control file closing

profile: use explicit logic to control file closing

We make the decision to close 'fp' more explicit instead of relying on the
implication of other variable. This makes the overall logic more robust.

--- a/mercurial/profiling.py	Mon Jun 12 17:13:35 2017 +0200
+++ b/mercurial/profiling.py	Mon Jun 12 17:14:56 2017 +0200
@@ -151,6 +151,7 @@
         self._ui = ui
         self._output = None
         self._fp = None
+        self._fpdoclose = True
         self._profiler = None
         self._enabled = enabled
         self._entered = False
@@ -193,6 +194,7 @@
             path = self._ui.expandpath(self._output)
             self._fp = open(path, 'wb')
         else:
+            self._fpdoclose = False
             self._fp = self._ui.ferr
 
         if proffn is not None:
@@ -221,4 +223,5 @@
             self._closefp()
 
     def _closefp(self):
-        self._fp.close()
+        if self._fpdoclose and self._fp is not None:
+            self._fp.close()